Such device is used, for example, in machines such as loaders for the movement of loads, and serves to actuate actuators having working cylinders, in which pistons are movably guided in accordance with a movement of the load that is to be moved. Depending on the positions of the pistons or actuators and the load moved thereby, an unfavorable shift in the balance point may lead to the tipping of the machine. To avoid tipping, these machines must meet the safety regulations laid out in the safety standard EN 15000, in particular. Accordingly, in the event of a risk of tipping, a movement that increases the load torque must be prevented, and a movement that reduces the load torque must be permitted. During the operation of the machine, a sudden shutdown of the consumers, in particular by intense braking decceleration may also cause a tipping of the machine. This problem has thus far been dealt with in that the allowable movement speed is reduced to reduce the braking decceleration. The movement speed is advantageously delayed proportional to the actuator position and to the load, or in other words, the movement is slowed. This slower movement is contrary to the user-side requirement of faster loading and unloading cycles. Alternatively, the movements of the two actuators can be permanently coupled in such a way that unwanted actuator positions are avoided.
In addition, uniform, “smooth” work are desirably made possible at the limits of the range of movement of the machine, or in other words, when the extreme positions of the actuators have been reached. For example, the flow divider, which is designed for a specific volume range, may be subject to leakage to such a degree that a fluid leakage flow is able to flow from one actuator that is allocated to a horizontal movement and that is subject to a higher pressure, to an actuator that is allocated to a vertical movement and that is subject to a lower pressure. The position of the additional actuator may be perceptibly influenced in the form of an irregularity in the in course of the movement, such as a “jolt”. This situation occurs in particular when the horizontally movable actuator is fully retracted and the vertically movable actuator is fully extended. The known devices for actuating hydraulic consumers such as the actuators, do not reliably suppress fluid leakage flow in this situation.
A device for actuating at least two hydraulic consumers is known from U.S. Pat. No. 5,473,828. The consumers are designed as hydraulic working cylinders, each having piston rod drives that can be extended different distances out of the cylinder housings for the purpose of actuating identically formed bucket halves of an excavator. Due to the different distances traveled by the piston rod drives, the bucket mechanism can be raised and break loose the remaining soil foundation when the bucket mechanism is closed and has penetrated a soil mass. The closed excavator bucket is tipped in that the longer working cylinder performs such a tipping movement.
To be able to hold the bucket halves in the closed position during the tipping or breaking-loose movement, a control line is provided downstream of a flow divider. The flow divider supplies the two sides of the piston of the working cylinders with hydraulic fluid, behind the flow divider pathway, which supplies the working cylinder having the smaller extension length. The control line controls a 3/2 directional control valve in such a way that, as the pressure increases when breaking loose from the ground, this valve goes to its closed position so that an additional influx of working fluid to this hydraulic cylinder is stopped and so that this cylinder is held in its position that closes the bucket mechanism, without an overload.
A control system for a fluid pressure actuating drive for controlling an adjustment of a predetermined fluid pressure actuating drive of at least two fluid pressure actuating drives as hydraulic consumers is known from DE 11 2005 001 879 T5. The flow of pressurized fluid of those actuating drives is provided by a common fluid pressure source and can be individually distributed by a flow divider device. Within the context of this individual distribution, an independent shut-off device is allocated to each hydraulic consumer, which shut-off devices can be actuated by a central control device. Operating states at the respective hydraulic consumers are monitored by a comprehensive sensor system and cause the control device to supply quantities of fluid to the consumers by the respective shut-off device in the form of valves, or to discharge such fluid from these consumers, preferably into a tank. As a result of this separate actuation regarding the respective hydraulic consumer, this known solution allows performing a fine adjustment or, respectively, fine positioning of the hydraulic consumers, for example in the form of hydraulic actuators. Moreover, such opportunity is created to automatically adapt the position or location of a working tool, for example in the form of an excavator bucket, in accordance with the location of another movable element, for example in the form of a hydraulically actuated load lifting arm. This known solution is structurally complex and a reliable control of fluid leak flows in the above mentioned context is not possible with this known solution.